During the following year, we shall continue our work with Escherichia coli topoisomerases-enzymes that catalyze the concerted breakage and reunion of DNA. We will try to prepare large quantities of E. coli DNA gyrase for physical and immunologic analysis. There are two different covalent complexes of DNA to gyrase and we want to determine the nature of the bonds and if the complex represents an obligatory reaction intermediate. We are particularly interested in the mechanism of energy transduction. We have discovered a new E. coli topoisomerase and we will study its enzymatic, physical, and functional properties. Finally, we are continuing our search for still more E. coli topoisomerases.